.308 barrel length and twist rates?

I''m new at this long range stuff, so to start, I am going the cheap route and getting a factory rifle in .308 to be used at 600 to 800 yards max. I'm leaning toward the Savage 10's but have researched other rifles and have a few questions. The Savage model 10's come with 20, 24 and 26 inch barrels with 1:10 twist rates. I have noticed that other varmint/tactical .308's come with a 1:12 twist and various lengths. My questions are, 1. What twist rate is better for accuracy at longer ranges? 2. Does the 1:12 twist allow for higher velocity than the 1:10? and 3. Does the .308 gain any performance with the longer barrel lengths? Basically, I'm looking for input on the best barrel length/twist combination, I need all the help I can get!! Thanks.

The twist rate has more to do with the ability to shoot longer bullets , the 1-12 will probably not stabilize the heavier bullets like the 200gr+VLD styles , which realy isin;t a problem as the 308 realy shines with the bullets in the 155-190 class. I personaly would get a 1-10 so if you wanted to play with the heavy bullets the option is their and I think your way better off over spinning a bullet than running it on the line as it will likely have stability issues if it falls into the subsonic range

As for barrel length , in the 308 a 20" barrel will give you all the speed thats needed to shoot 175gr bullet out past 1000yds , but unless weight and the length of the barrel are gonna get in the way I say use the longest barrel available as you will gain a little bit of speed not very much with the 308 but if you decide to use the heavy 190+gr bullets the extra length will allow you to use slower powders and get the most out of the round.

The Heavy barreled remingtons are typicaly pretty accurate and you will have a good base to build on later if you choose.
the Savages will probably shoot a little bit more accurately than the Rem as their barrels are a bit better quality , and if the rifle you get is a long action it realy opens the options if you rebuild later.
In either case the 308 is a great round to start off with as their are alot of quality rounds out their in factory form if you don't reload , it has a very long barrel life , very easy to load for , don't recoil much and on and on.